Water-resistant nonfibrous regenerated cellulose film and process of producing same



United States Patent Q WATER-RESISTANT NONFIBROUS REGENERATED CELLULGSEFILM AND PROCESS OF PRODUC- ING SAME Gerald I. Keim, West Grove, Pa.,assignor to Hercules Powder Company, Wilmington, Del., a corporation ofDelaware N Drawing. Filed Mar. 12, 1958, Ser. No. 720,812

1 Claim. (Cl. 117-72) This invention relates to the treatment ofnonfibrous regenerated cellulose film to improve the bonding of saidfilm to the subsequently applied topcoat.

Non fibrous regenerated cellulose films have found utility in thepackaging of various products to protect them against the deleteriouseifects of atmospheric moisture. To adapt them for this use, such areconventionally provided with a water-repellent topcoat adhesivelysecured thereto by a suitable anchoring agent. One of the frequentdisadvantages encountered in the use of these treated films for theindicated purpose is that the anchoring agent breaks down after a periodof exposure to moist atmospheric conditions, particularly at higherrelative humidities. As a result, the adhesive bond between thenonfibrous regenerated film and the water-repellent topcoat is weakenedor broken, thereby permitting the entry of moisture into the packagewith consequent adverse effects on the packaged product.

A principal object of the present invention is the pro vision of aprocess for anchoring nonfibrous regenerated cellulose film to awater-repellent topcoat whereby a film having prolonged resistance tomoisture and moisture vapor transmission is obtained.

A further and more specific object of the invention is the provision ofa film of the indicated type wherein the nonfibrous regeneratedcellulose film is anchored to the water-repellent topcoat by a novel andhighly effective anchoring agent.

Another object of the invention is the provision of an anchor coatingfor nonfibrous regenerated cellulose film having greater tenacity anddurability than prior art anchor coatings, which may be obtained in ashorter time of immersion in a bath or by spray and which, when dried,furnishes a nonblocking, heat-scalable film that retains its originaldimensional stability, flexibility and appearance after coating.

In accordance with the invention, 'the above and other objects areaccomplished by utilizing as the anchoring agent a thermosettingcationic resin comprising a watersoluble polymeric reaction product ofepichlorohydrin and a polyamide derived from a polyalkylene polyamineand a C -C saturated aliphatic dicarboxylic acid.

In carrying out the process of the invention, an aqueous solution of thecationic resin may be applied to a nonfibrous regenerated cellulosefilm, as by dipping or spraying, and the treated film then dried by anyof the commercially available methods of drying such as by passing itover hot rolls or through heated tunnels or by exposure to infraredlamps, etc. Alternatively, since the cationic resin utilized herein iscompatible with and soluble in a viscose solution, it may beincorporated in the film during manufacture thereof as by adding anaqueous solution of the resin to the viscose solution. After the filmhas been dried, a moisture-resistant topcoat is applied in the usualmanner.

The aqueous resin solutions contemplated for use herein are dilutable toany desired concentration in water. Hence, they may be applied tononfibrous regenerated cellulose film at anydesired or convenientconcentration. From an economic standpoint, it is desirable to use theseresins in solutions varying from about 0.1% to about However, if it isdesired, for example, to decrease 3,039,889 Patented June 19, 19-82 icethe time required for cure, the resin solution may be increased insolids to about 40% provided it is used promptly, i.e., within about anhour after such concentration.

The amount of resin in or on the film will vary depending on the degreeof anchoring desired and other factors. In some cases, as little as 1.0%by weight, based on the weight of the film, will suffice. In othercases, more or less may be desirable. In general, amounts above about10.0% afford little, if any, added advantage and, hence, will notordinarliy be used. The figures given are intended to serve as a guideand should not be construed as limiting the scope of the invention sincethe amount needed for a particular application is readily determinableby one skilled in the art.

The resins herein disclosed are highly cationic and, when added to aviscose solution and the latter then processed into film, are largelyretained by the cellulose and carried through into the finished film.Some losses, however, are inevitable and allowance should be made forthese when this procedure is utilized.

In the processing of unplasticized nonfibrous regenerated cellulosefilm, it is conventional practice to treat the film with glycerin orother polyol plasticizer commonly used for this purpose. The aqueousresin solutions of the present invention are compatible with suchplasticizers in all proportions and, hence, the two may be mixedtogether and applied to, or incorporated in, the film in one step. Suchresins, moreover, do not precipitate from the glycerol or likeapplication bath in the presence of inorganic salts carried over fromthe acid regeneration bath.

In the preparation of the cationic thermosetting resins contemplated foruse herein, the dicarboxylic acid is first reacted with the polyalkylenepolyamine under conditions such as to produce a Water-soluble polyamidecontaining the recurring groups where n and x are each 2 or more and Ris the divalent hydrocarbon radical of the dicarboxylic acid. Thiswatersoluble polyamide is then reacted with epichlorohydrin' to form thewater-soluble cationic thermosetting resin.

The dicarboxylic acids contemplated for use in preparing these resinsare the C -C saturated aliphatic dicarboxylic acids such as succinic,glutaric, adipic and the like. The saturated dicarboxylic acids havingfrom 4 to 8 carbon atoms in the molecule are preferred. Blends of two ormore of the saturated dicarboxylic acids may also be used.

A variety of polyalkylene polyamines including" polyethylene polyamincs,polypropylene poly amines, polybutylene poly-amines and so on may beemployed of which the polyethylene polyamines represent an economicallypreferred class. More specifically, the polyalkylene polyaminescontemplated for use may be represented as polyamines in which thenitrogen atoms are linked together by groups of the formula --C,,H wheren is a small integer greater than unity and the number of such groups inthe molecule ranges from two up to about eight. The nitrogen atoms maybe attached to adjacent carbon atoms in the group C H or to carbon atomsfurther apart, but not to the same carbon atom. This inventioncontemplates not only the use of such polyarrn'nes asdiethylenetriamine, triethylenetetramine, tetraethylenepent amine,dipropylenetriamine and the like, which can be obtained in reasonablypure form, but also mixtures and various crude polyamine materials. Forexample, the mixture of polyethylene polyamines obtained by the reactionof ammonia and ethylene dichloride, refined only to the extent ofremoval of chlorides, water, excess amrnom'a and ethylenediamine, is avery satisfactory start-l ing material. The term polyalkylene polyamineemployed in the claims, therefore, refers to and includes any of thepolyalkylene pclyamines referred to above or to a mixture of suchpolyalkylene polyamines.

It is desirable, in some cases, to increase the spacing of secondaryamino groups on the polyarnide molecule in order to change thereactivity of the pol-yamide-epichlorohydrin complex. This can beaccomplished by substituting a diamine such as ethylenediamine,propylenediamine, hexamethylenediamine and the like for a portion of thepolyalkylene polyamine. For this purpose, up to about 80% of thepolyalkylene polyamine may be replaced by a molecularly equivalentamount of the diamine. Usually, a replacement of about 50% or less willserve the purpose.

The temperatures employed for carrying out the reaction between thedicarboxylic acid and the polyalkylene polyamine may vary from about 110C. to about 250 C. or higher at atmospheric pressure. For most purposes,however, temperatures between about 160 C. and 210 C. have been foundsatisfactory and are preferred. Where reduced pressures are employed,somewhat lower temperatures may be utilized. The time of reactiondepends on the temperatures and pressures utilized and will ordinarilyvary from about /2 to 2 hours, although shorter or longer reaction timesmay be utilized depending on reaction conditions. In any event, thereaction is desirably continued to substantial completion for bestresults.

'In carrying out the reaction, it is preferred to use an amount ofdicarboxylic acid suflicient to react substantially completely with theprimary amine groups of the polyalkylene polyamine but insufficient toreact with the secondary amine groups to any substantial extent. Thiswill usually require a mole ratio of polyalkylene polyamine todicarboxylic acid of from about 0.9:1 to about 1.2: 1. However, moleratios of from about 0.8 :1 to about 1.4:1 may be used with quitesatisfactory results. Mole ratios outside of these ranges are generallyunsatisfactory. Thus, mole ratios below about 0.8:1 result in a gelledproduct or one having a pronounced tendency to gel while mole ratiosabove 1.4:1 result in low molecular weight polyamides. Such productswhen reacted with epichlorohydrin, do not produce resins having thedesired efficiency for use herein.

In converting the polyamide, formed as above described, to a cationicthermosetting resin, it is reacted with epichlorohydrin at a temperaturefrom about 45 C. to about 100 C. and preferably between about 45 C. and70 C. until the viscosity of a 20% solids solution at 25 C. has reachedabout C or higher on the Gardner-Holdt scale. This reaction ispreferably carried out in aqueous solution to moderate the reaction. pHadjustment is usually not necessary. However, since the pH decreasesduring the polymerization phase of the reaction it may be desirable, insome cases, to add alkali to combine with at least some of the acidformed.

When the desired viscosity is reached, sufiicient water is then added toadjust the solids content of the resin solu tion to the desired amount,i.e., about more or less, the product cooled to about 25 C. and thenstabilized by adding sufficient acid to reduce the pH at least to about6 and preferably to about 5. Any suitable acid such as hydrochloric,sulfuric, nitric, formic, phosphoric and acetic acid may be used .tostabilize the product. However, bydrochloric acid is preferred.

In the polyamide-epichlorohydrin reaction, it is preferred to usesufiicient epichlorohydrin to convert all secondary amine groups totertiary amine groups. However, more or less may be added to moderate orincrease reaction rates. In general, satisfactory results may beobtained utilizing from about 0.5 mole to about 1.8 moles ofepichlorohydrin for each secondary amine group of the polyamide. It ispreferred to utilize from about 1.0 mole to about 1.5 moles for eachsecondary amine group of the polyamide.

The following examples will serve to illustrate the invention. In theseexamples, the cationic water-soluble 4 thermosettingpolyamide-epichlorohydrin resin utilized was prepared as follows.

0.97 mole of diethylene triamine and suificient water for slurry wereplaced in a flask equipped with a mechanical stirrer, thermometer andcondenser. To this was added 1.0 mole of adipic acid. After the acid haddissolved in the amine, the solution was heated to 195 C. and held therefor 1 /2 hours. The mixture was then cooled under atmospheric pressureto 140 C., and sufficient water added so that the resulting solutioncontained approximately 50% solids.

To a given amount of the above polyamide solution, sufiicient water wasadded to lower the percent solids to approximately 25%. This solutionwas heated to 50 C., and an amount of epichlorohydrin sufficient to givea ratio of 1.15 moles of epichlorohydrin to 1 mole of secondary amine inthe polyamide, was added dropwise over a period of 1015 minutes. Thecontents of the flask were then heated at a temperature of 60-70 C.until it had attained a Gardner viscosity of D-E. Sufficient water wasthen added to the product to achieve a percent solids of approximately10% and it was cooled to 25 C. Suflicient 10% HCl was added to adjustthe pH to 5.05.5. The final product contained 9.6% solids and had aGardner viscosity of C-D.

Example 1 An aqueous solution of the cationic polyamide-epichlorohydrinresin, prepared as above described, and containing 9.6% solids wasapplied to plasticized cellophane by means of conventional sprayequipment and dried in a forced draft oven at C. After 15 minutes dryingtime, the film was unwrinkled, nontacky, nonblocking, transparent andlustrous. Spraying was done to both sides in such a way that a filmthickness of 0.1 mil (0.0001 inch) of dried coating was obtained.

The film was subsequently sprayed with a nitrocellulosebased coatingsimilar to that described in US. Patent 2,236,546 and dried for 30minutes at 66 C. A film thus prepared was immersed in water. Similarly,a film with no anchor coating, but bearing the nitrocellulose coating,was immersed in water. The film bearing both the cationic resin-anchorcoat, and nitrocellulose coat, remained unchanged after four weeksimmersion, whereas the film to which no anchor coat and a nitrocelluloselacquer had been applied blushed badly after only 1 hour. The tensileproperties of the resin-coated film were the same as those of anuncoated, plasticized cellophane.

Example 2 A plasticized untreated cellophane film was dip coated in a9.6% solids water solution of the cationic resin, prepared as abovedescribed, for 2 minutes, allowed to drain and the film then heated for2 hours under a pressure of 10 mm. of Hg at 65 C. Films which had beenso treated and subsequently sprayed with a protective moistureresistantnitrocellulose lacquer coating and dried, as in Example 1, possessed amoisture vapor transmission rate of 4.2-4.9 g./24 hrs./ sq. m., whereasfilms which had received no anchor coating but had received a spraycoating of nitrocellulose lacquer, possessed a moisture vaportransmission of 6-8 g./24 hrs/sq. m.

Example 3 The procedure outlined in Example 1 was followed except that a9.6% solids aqueous solution of the cationic resin and 10% by weight,based on the weight of solution of cationic resin, of glycerin wasapplied by means of spray equipment to unplasticized cellophane. Afterprolonged immersion, the film bearing both the resin-anchor coat and thenitrocellulose coat remained unchanged.

Examples 4 and 5 The procedure of Example 3 was followed except that theaqueous solution contained 1% of the cationic resin and 20% of glycerin(Example 4) and 0.3% of the cationic resin and 6% of glycerin (Example5). In each case, the results obtained were comparable to those obtainedin Examples 1 and 3.

Example 6 The procedure of Example 1 was followed except the aqueoussolution contained 9.6% resin plus glycerin and application tounplasticized cellophane was made by dip coating and the use of niprolls so that the applied coating was approximately 0.1 mil thick aftercuring. The results obtained were comparable to those obtained in thepreceding examples.

Examples 7 and 8 The procedure of Example 6 was followed except that theaqueous solution contained 1% resin and 20% glycerin (Example '7) and0.3% resin and 6% glycerin (Example 8). The results were comparable tothose previously obtained.

The time of immersion required for dip coating procedures such as thoseutilized in Examples 6 to 8 is relatively short, being of the order offrom about 1 minute to about 5 minutes. For resin film thicknesses lessthan about 0.1 mil, i.e., of the order of 0.01 mil or less, somewhatshorter periods of immersion may be utilized.

Any of the well-known water-repellent coating compositions or lacquerswhich are applied to regenerated cellulose films may be utilized herein.Customarily such lacquers comprise a film-former such as cellulosenitrate, ethyl cellulose, chlorinated rubber, etc., a plasticizer forthe film-former, a moistureproofing agent such as paraflin wax, ablending agent, volatile solvents, etc. Examples of typicalmoistureproofing compositions may be found in U.S. 1,737,187 (Charch andPrindle), U.S. 1,997,583

10 at least one secondary amine group with a C -C saturated aliphaticdicarboxylic acid at a temperature from about 110 C. to about 250 C. andin a mole ratio of polyalkylene polyamine to dicarboxylic acid of fromabout 0.8 to 1 to about 1.4 to 1 to form a water-soluble long-chainpolyamide containing secondary amine groups, and then reacting thepolyamide in aqueous solution with epichlorohydrin at a temperature fromabout 45 C. to about 100 C. and in a mole ratio of epichlorohyd-rin tosecondary amine groups of said polyamide of from about 0.5 to 1 to about1.8 to 1.

References Cited in the file of this patent UNITED STATES PATENTS2,573,956 Daniel et a1 Nov. 6, 1951 2,630,397 Cowan et a1 Mar. 3, 19532,926,154 Kcin'l Feb. 23, 1960 FOREIGN PATENTS 610,311 Great BritainOct. 14, 1948 529,729 Canada Aug. 28, 1956 OTHER REFERENCES Ser. No.323,512, Hagedorn (A.P.C.), published April

